1. Field of the Invention
The invention in general relates to electrostrictive transducers and particularly to electrostrictive transducers which produce fan-shaped beams.
2. Description of the Prior Art
In many situations it is desirable for a sonar system to use a transducer which will produce a fan-shaped beam, that is, a beam which is relatively narrow in one dimension and relatively broad in another dimension. These transducers find application in various systems such as in a side looking sonar system, wherein the transducer, mounted on a carrier vehicle, produces a fan-shaped beam aimed out to the side of the carrier with a typical horizontal transducer beamwidth of a few tenths of a degree and a typical vertical transducer beamwidth of 70.degree. to 75.degree. (measured at the 3 dB points) by way of example.
For some applications of a fan-shaped beam, there is a requirement for a much broader vertical breamwidth, for example 150.degree. or greater and the available side looking sonar transducers are not capable of forming such beam.
One well known method for achieving a very broad beamwidth for a line transducer is to use piezoelectric tubes as the active elements. These tubes, axially arranged, can produce an omnidirectional beam pattern in the plane perpendicular to the tube axis. At relatively high frequencies, for example in the hundreds of kilohertz, it is extremely difficult to obtain high quality tubular active elements which radiate (or respond) uniformly in the radial direction. In addition to the high costs of such tubes, an added expense occurs if the tubes are not all exactly tuned to the desired operating frequency. In such instance, the outside diameters of the tube must be reduced necessitating first a removal of the electrode covering the outer surface of the tube and then a replacement thereof after the reduction in size.